Resubmission Systemic lupus erythematosus (SLE) is much more prevalent in females than males in humans, and in the (NZBxNZW)F1 (BWF1) mouse model of lupus. Although estrogens can exacerbate disease in females, considerable evidence suggests that androgens play a critical role in protecting males from lupus in both humans and mice. The gut microbiota is now thought to play a major role in host health and disease, and microbiota dysbiosis is associated with development of autoimmune diseases. Interestingly, androgens can have a significant impact on the microbiota and vice versa. Recent studies in a mouse model of type 1 diabetes (T1D) suggest that the microbiota and androgens collaborate, in what is now being referred to as the microgenderome, to protect male mice from disease via currently unknown mechanisms. However, little is known about the relationship between androgens and the microbiota in lupus. In preliminary studies, we have found that both the microbiota composition and metabolomic profile differ significantly between mature female and male BWF1 mice, and transfer of male microbiota to female BWF1 mice protects female recipients from disease, and significantly enhances survival. These data suggest that the male environment confers protective properties on the microbiota by altering microbiota composition and/or metabolome. Metabolites from commensal bacteria have been found to induce Treg differentiation both directly and through DC. The gut CD103+ dendritic cells (CD103DC) are highly tolerogenic, and generate regulatory T cells in the periphery that can control systemic immune responses. Our preliminary data showing sex-based differences in CD103DC function, and the requirement for CD103+ cells for protection in male BWF1 mice strongly support the notion that CD103DC function as a critical link between the male gut microbiota and the immune response, and may, therefore, play an important role in protecting BWF1 male mice from disease. Moreover, preliminary analysis of the microbiota metabolome has identified a metabolite that is increased in male BWF1 mice that may have an impact CD103DC function. We, therefore, hypothesize that the androgen-modified male microbiota and its metabolites protect against lupus by acting through the gut CD103DC. This novel hypothesis will be addressed in lupus-prone BWF1 mice by 1) examining the impact of androgens on the gut microbiota and its metabolites; 2) exploring the role of male microbiota and its metabolites in protection from disease; and 3) determining the role that CD103DC play in male microbiota- mediated protection from disease. The proposed project will fill the gaps in our knowledge about the role of the androgen-gut microbiota relationship in immunoregulation and lupus, and will lead to the development of novel therapeutic strategies using the microbiota and/or its metabolites for the treatment of lupus and other autoimmune diseases.